Watch out for RAID systems. I have an on-board RAID controller and it chopped my sound to pieces when i recorded. After fighting with this problem for a month or two i disabled my RAID-controller and put my hard-disks on the normal ATA133 bus instead. Now everything works fine. I also heard about people having trouble with SATA-systems but i don?t have any experience with this. If you dicide to build a system yourself check this page first:
http://www.pcmus.com/. I found it very usefull when having trouble with my sound...